Micelles are typically referred to as a spherical structure which is thermodynamically stable and of uniform form by low-molecular-weight materials having amphiphilic groups, that is, both hydrophilic and hydrophobic groups at the same time. In the case where a solution of the water-insoluble medicine in a compound having the micelle structure is introduced, the medicine is located inside the micelles, and such micelles are capable of carrying out the release of a target-oriented medicine in response to changes in temperature or pH in vivo and are thus regarded as having very high applicability as carriers for the delivery of medicines.
Korean Patent Application No. 10-2001-0035265 discloses the formation of micelles using poly(ethylene glycol) and a biodegradable polymer. These materials which are biodegradable are advantageous because they have biocompatibility, but are not sensitive to changes in vivo, for example, changes in pH, making it difficult to deliver the medicine to the desired sites.
Meanwhile, the pH condition in vivo typically falls in the pH range of 7.4˜7.2, whereas the condition around abnormal cells such as cancer cells is known to be weak or strongly acidic in the pH range of 3.0˜7.0. Recently, in order to deliver medicines specific to cancer cells, research into releasing medicines at a pH of 7.0 or less is ongoing.
U.S. Pat. No. 5,955,509 entitled “pH dependent polymer micelles” discloses a method of manufacturing pH-sensitive polymer micelles in which a block copolymer of poly(vinyl N-heterocycle) and poly(alkylene oxide) forms micelles at a pH of 6.0 or above and the micelles break down at a pH of 2˜6, and Japanese Patent Publication No. 2002-179556, entitled “block copolymer-anticancer agent combined drug formulation” discloses a block copolymer of a hydrophilic poly(ethylene glycol) based compound and a hydrophobic polyamino acid based compound, which forms micelles at a specific pH.